A radar device transmits a high-frequency radar transmission signal from a measurement point to a space, receives a reflected wave signal reflected by the target, and measures at least one of the distance between the measurement point and the target and a direction in which the target is present (direction of arrival). In recent years, development of a radar device that estimates a direction of arrival or a distance to the target including a vehicle and a pedestrian by performing high-resolution measurement using a radar transmission signal with a short wavelength including a microwave or a millimeter wave has been carried out.
The radar device receives mixed signals of respective reflected waves from a target present at a short distance and a target present at a long distance. A range side lobe occurs in the reflected wave signal from the target present at a short distance. When the range side lobe and the main lobe of the reflected wave signal from the target present at a long distance are mixed, the detection accuracy of the target present at a long distance is degraded.
Therefore, it is required for the radar device, for which high-resolution measurement is required for a plurality of targets, to transmit a pulse wave or a pulse modulated wave using a transmission code having an autocorrelation characteristic for a low range side lobe level (hereinafter, referred to as a “low range side lobe characteristic”).
When a vehicle and a pedestrian are present at the same distance from the measurement point, the radar device receives mixed signals of respective reflected wave signals from the vehicle and the pedestrian whose radar cross sections (RCS) are different. The radar cross section of the pedestrian is smaller than the radar cross section of the vehicle. That is, the signal level of the reflected wave signal changes with the distance or type of the target.
In contrast, even if a vehicle and a pedestrian are present at the same distance from the measurement point, the radar device is required to properly receive the respective reflected wave signals from the vehicle and the pedestrian. For this reason, the radar device is required to have a wide receiving dynamic range to the extent of receiving reflected wave signals having various signal levels.
For example, PTL 1 is known as a related art to detect a plurality of targets simultaneously with high azimuth resolution using a small number of antennas.